The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A multi-RAT cellular network refers to a cellular network in which one or more radio access technologies are used for signals between mobile devices and base stations. A mobile device can move between coverage areas deploying respective RATs. Each coverage area has an associated cell. A cell can have one or more assigned carrier frequencies on which signals are transmitted between the mobile device and base stations in the corresponding coverage area of that cell.
As an example, cellular networks can deploy RATs such as second generation (2G), third generation (3G), and/or fourth generation (4G) long term evolution (LTE) wireless communication technologies. Third generation partnership project (3GPP) networks can deploy, for example, (i) universal mobile telecommunication system (UMTS) terrestrial radio access (UTRAN) for 2G and 3G communication between a mobile device and a base station, and (ii) evolved UTRAN (EUTRAN) for 4 G communication between a mobile device and a base station.
A mobile device (also referred to as a user equipment or UE) can be equipped with multi-RAT transmit and receive capabilities. The mobile device can move across cells having different deployed RATs. The mobile device can communicate with (i) a first base station in a first cell using a first RAT, and (ii) a second base station in a second cell using a second RAT. Since the mobile device is moving between cells in which different RATs are deployed, an inter-RAT handover is performed from the first base station to the second base station.
During inter-RAT handover, selection of a new or different cell (referred to as cell reselection) can be controlled by (i) the base stations via a “backbone” network when the mobile device is operating in a connected mode, or (ii) the mobile device when the mobile device is operating in an idle mode. The base stations can communicate with each other via the backbone network. While in the idle mode, the mobile device can perform cell reselection if conditions of one or more channels of a current cell deteriorate. A channel can be considered as deteriorated when one or more conditions exist, for example, when one or more parameters are outside predetermined ranges. The parameters can include signal-to-noise ratio (SNR), bit error rate (BER), number of errors, signal quality, etc. A handover and cell reselection can be performed to allow a mobile device to receive system information blocks (SIBs), perform random access procedures to connect to a base station, and receive paging messages from a base station. SIBs can be in system information messages periodically transmitted from base stations to mobile devices.